1. Field of the Invention
This invention relates to floating vessels. More particularly, it relates to platform-type semisubmersible vessels
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A semi-submersible is a particular type of floating vessel that is supported primarily on large pontoon-like structures submerged below the sea surface. The operating decks are typically elevated about 100 or more feet above the pontoons on steel columns. This design has the advantage of submerging most of the area of the components in contact with the sea and minimizing loading from waves and wind. Semisubmersibles can operate in a wide range of water depths, including deep water. They are usually anchored with six to twelve anchors tethered by chains and/or wire cables, which are computer controlled to maintain stationkeeping. Semi-submersibles (or “semis”) can be used for drilling, workover operations, and production platforms, depending on the equipment with which they are equipped. When fitted with a drilling package, they may be called semisubmersible drilling rigs.
As shown in FIG. 1, a semi-submersible hull 100 of the prior art commonly has columns 102 at the corners of the vessel that are rectangular in cross section. Each column is attached to two pontoons 104 which extend between adjacent columns. Central opening 106 is defined by pontoons 104. Typically, a deck (not shown) is support on upper surface 108 of columns 102.
Certain semi-submersibles of the prior art have columns that are rectangular (four faces per column) and are positioned such that the column faces (sides) are set at 45 degrees with respect to the longitudinal axis of the adjoining pontoon.
The column shape of the present invention is similar to that of the “EXMAR OPTI-EX” semi-submersible illustrated in FIG. 2. However, in the case of that semi-submersible, the non-orthogonal fifth-face of each column is oriented towards the interior of the semi-submersible rather than the exterior.